Specific heat evidence for two-gap superconductivity in ternary-iron silicide Lu2_{2}Fe3_{3}Si5_{5}

We report low-temperature specific heat studies on single-crystalline ternary-iron silicide superconductor Lu$_{2}$Fe$_{3}$Si$_{5}$ with$T_c$ = 6.1 K down to $\sim T_c/20$. We confirm a reduced normalized jump in specific heat at $T_c$, and find that the specific heat divided by temperature $C/T$ shows sudden drop at $\sim T_c/5$ and goes to zero with further decreasing temperature. These results indicate the presence of two distinct superconducting gaps in Lu$_{2}$Fe$_{3}$Si$_{5}$, similar to a typical two-gap superconductor MgB$_{2}$. We also report Hall coefficients, band structure calculation, and the anisotropy of upper critical fields for Lu$_{2}$Fe$_{3}$Si$_{5}$, which support the anisotropic multiband nature and reinforce the existence of two superconducting gaps in Lu$_{2}$Fe$_{3}$Si$_{5}$.Comment: 5 pages, 5 figure

Disorder-sensitive superconductivity in the iron silicide Lu2_2Fe3_3Si5_5 studied by the Lu-site substitutions

We studied effect of non-magnetic and magnetic impurities on superconductivity in Lu$_2$Fe$_3$Si$_5$ by small amount substitution of the Lu site, which investigated structural, magnetic, and electrical properties of non-magnetic (Lu$_{1-x}$Sc$_x$)$_2$Fe$_3$Si$_5$, (Lu$_{1-x}$Y$_x$)$_2$Fe$_3$Si$_5$, and magnetic (Lu$_{1-x}$Dy$_x$)$_2$Fe$_3$Si$_5$. The rapid depression of $T_c$ by non-magnetic impurities in accordance with the increase of residual resistivity reveals the strong pair breaking dominated by disorder. We provide compelling evidence for the sign reversal of the superconducting order parameter in Lu$_2$Fe$_3$Si$_5$.Comment: 4 pages, 5 figure

Semiótica y Teatro

Viene fornito neU'articolo il modello della comunicazione teatrale, mediante un confronto con la comunicazione narrativa. In sostanza, la comunicazione teatrale é perpendicolare a quella che si svolge tra i personaggi in scena (che infatti usano i pronomi IO/TU come se fossero soggetti autonomi, mentre il rapporto tra emitiente e ricevente del testo é occultato); invece la comunicazione narrativa collega orizzontalmente 1'emitiente e il ricevente, trasmettendo il testo tramite un narratore implícito o esplicito, che designa i personaggi con la terza persona. E'solo con la mediazone di questa terza persona che viene comunicato talora, attraverso i discorsi diretti, il dialogo IO/TU dei personaggi. The article deals with the model of theatre communication and compares it with narrative communication model. Substancially, theatre communication is perpendicular to the one of the characters on the scene (in fact characters use the pronouns I/YOU as if they were autonomous subjects, while the relationshíp between the addressee of the text is concealed). On the other hand of narrative communication horizontally connects the addresser and the addressee by transferring the text through an implicit narrator who indicates the characters with the third person that sometimes the dialogue I/YOU of the characters is delivered through direct speaches

The Finite Field Kakeya Problem

A Besicovitch set in AG(n,q) is a set of points containing a line in every direction. The Kakeya problem is to determine the minimal size of such a set. We solve the Kakeya problem in the plane, and substantially improve the known bounds for n greater than 4.Comment: 13 page

Extinction efficiencies of coated absorbing aerosols measured by cavity ring down aerosol spectrometry

International audienceIn this study, we measure the extinction efficiency at 532 nm of absorbing aerosol particles coated with a non-absorbing solid and liquid organic shell with coating thickness varying between 5 and 100 nm using cavity ring down aerosol spectrometry. For this purpose, we use nigrosin, an organic black dye, as a model absorbing core and two non-absorbing organic substances as shells, glutaric acid (GA) and Di-Ethyl-Hexyl-Sebacate (DEHS). The measured behavior of the coated particles is consistent with Mie calculations of core-shell particles. Errors between measured and calculated values for nigrosin coated with GA and DEHS are between 0.5% and 10.5% and between 0.5% and 9%, respectively. However, it is evident that the calculations are in better agreement with the measured results for thinner coatings. Possible reasons for these discrepancies are discussed

Shear-induced quench of long-range correlations in a liquid mixture

A static correlation function of concentration fluctuations in a (dilute) binary liquid mixture subjected to both a concentration gradient and uniform shear flow is investigated within the framework of fluctuating hydrodynamics. It is shown that a well-known $|\nabla c|^2/k^4$ long-range correlation at large wave numbers $k$ crosses over to a weaker divergent one for wave numbers satisfying $k<(\dot{\gamma}/D)^{1/2}$, while an asymptotic shear-controlled power-law dependence is confirmed at much smaller wave numbers given by $k\ll (\dot{\gamma}/\nu)^{1/2}$, where $c$, $\dot{\gamma}$, $D$ and $\nu$ are the mass concentration, the rate of the shear, the mass diffusivity and the kinematic viscosity of the mixture, respectively. The result will provide for the first time the possibility to observe the shear-induced suppression of a long-range correlation experimentally by using, for example, a low-angle light scattering technique.Comment: 8pages, 2figure

Surfaces containing a family of plane curves not forming a fibration

We complete the classification of smooth surfaces swept out by a 1-dimensional family of plane curves that do not form a fibration. As a consequence, we characterize manifolds swept out by a 1-dimensional family of hypersurfaces that do not form a fibration.Comment: Author's post-print, final version published online in Collect. Mat

Free-energy transition in a gas of non-interacting nonlinear wave-particles

We investigate the dynamics of a gas of non-interacting particle-like soliton waves, demonstrating that phase transitions originate from their collective behavior. This is predicted by solving exactly the nonlinear equations and by employing methods of the statistical mechanics of chaos. In particular, we show that a suitable free energy undergoes a metamorphosis as the input excitation is increased, thereby developing a first order phase transition whose measurable manifestation is the formation of shock waves. This demonstrates that even the simplest phase-space dynamics, involving independent (uncoupled) degrees of freedom, can sustain critical phenomena.Comment: 4 pages, 3 figure